Capacitor construction

ABSTRACT

A method of forming a capacitor includes, a) providing a node to which electrical connection to a capacitor is to be made; b) providing a first electrically conductive capacitor plate over the node, the capacitor plate comprising conductively doped polysilicon; c) providing a predominately amorphous electrically conductive layer over the first capacitor plate; d) providing a capacitor dielectric layer over the amorphous electrically conductive layer; and e) providing a second electrically conductive capacitor plate over the capacitor dielectric layer. A capacitor construction is also disclosed. The invention has greatest utility where the polysilicon layer covered with the amorphous conductive layer is a roughened outer layer, such as provided with hemispherical grain polysilicon. The preferred amorphous electrically conductive layer is metal organic chemical vapor deposited TiC x  N y  O z , where &#34;x&#34; is in the range of from 0.01 to 0.5, and &#34;y&#34; is in the range of from 0.99 to 0.5, and &#34;z&#34; is in the range of from 0 to 0.3, with the sum of &#34;x&#34;, &#34;y&#34; and &#34;z&#34; equalling about 1.0; and the step of metal organic chemical vapor depositing TiC x  N y  O z  comprises utilizing a gaseous titanium organometallic precursor of the formula Ti(NR 2 ) 4 , where R is selected from the group consisting of H and a carbon containing radical, and utilizing deposition conditions of from 200° C. to 600° C. and from 0.1 to 100 Torr.

RELATED PATENT DATA

This is a divisional application claiming priority to U.S. patentapplication Ser. No. 08/666,896, filed Jun. 19, 1996, by Gurtej S.Sandhu et al., entitled "Method of Forming Capacitors and CapacitorConstruction" and which claims priority to U.S. patent application Ser.No. 08/444,852, filed May 19, 1995, by Gurtej S. Sandhu et al, entitled"Method of Forming Capacitors Having an Amorphous ElectricallyConductive Layer", now U.S. Pat. No. 5,665,625.

TECHNICAL FIELD

This invention relates generally to semiconductor processing methods offorming capacitors and to capacitor constructions.

BACKGROUND OF THE INVENTION

The reduction in memory cell size required for high density dynamicrandom access memories (DRAMs) results in a corresponding decrease inthe area available for the storage node of the memory cell capacitor.Yet, design and operational parameters determine the minimum chargerequired for reliable operation of the memory cell despite decreasingcell area. Several techniques have been developed to increase the totalcharge capacity of the cell capacitor without significantly affectingthe cell area. These include structures utilizing trench and stackedcapacitors, as well as the utilization of new capacitor dielectricmaterials having higher dielectric constants.

One common material utilized for capacitor plates is conductively dopedpolysilicon. Such is utilized because of its compatibility withsubsequent high temperature processing, good thermal expansionproperties with SiO₂, and its ability to be conformally deposited overwidely varying typography.

As background, silicon occurs in crystalline and amorphous forms.Further, there are two basic types of crystalline silicon known asmonocrystalline silicon and polycrystalline silicon. Polycrystallinesilicon, polysilicon for short, is typically in situ or subsequentlyconductively doped to render the material conductive. Monocrystallinesilicon is typically epitaxially grown from a silicon substrate. Siliconfilms deposited on dielectrics (such as SiO₂ and Si₃ N₄) result ineither an amorphous or polycrystalline phase. Specifically, it isgenerally known within the prior art that silicon deposited at wafertemperatures of less than approximately 580° C. will result in anamorphous silicon layer, whereas silicon deposited at temperatureshigher than about 580° C. will result in a polycrystalline layer. Thespecific transition temperature depends on the sourcechemicals/precursors used for the deposition.

The prior art has recognized that capacitance of a polysilicon layer canbe increased merely by increasing the surface roughness of thepolysilicon film that is used as a capacitor storage node. Suchroughness is typically transferred to the cell dielectric and overlyingpolysilicon layer interfaces, resulting in a larger surface area for theis same planar area which is available for the capacitor. One procedureutilized to achieve surface roughening involves deposition underconditions which are intended to inherently induce a rough or ruggedupper polysilicon surface. Such include low pressure chemical vapordeposition (LPCVD) techniques. Yet, such techniques are inherentlyunpredictable or inconsistent in the production of a rugged polysiliconfilm.

One type of polysilicon film which maximizes a roughened outer surfacearea is hemispherical grain polysilicon. Such can be deposited or grownby a number of techniques. One technique includes direct LPCVD formationat 590° C. Another includes formation by first depositing an amorphoussilicon film at 550° C. using He diluted SiH₄ (20%) gas at 1.0 Torr,followed by a subsequent high temperature transformation anneal.Hemispherical grain polysilicon is not, however, in situ doped duringits deposition due to undesired reduction in grain size in the resultantfilm. Accordingly, doping after deposition is typically conducted withhemispherical grain polysilicon films.

Unfortunately, roughened polysilicon films suffer from dopant depletionwhereby the conductivity dopant moves outwardly into the adjacentcapacitor dielectric layer. Further, roughened polysilicon films have aconsiderable number of exposed crystalline triple points, whichconstitute locations where three individual crystals join. These triplepoints result in formation or propagation of cracks throughout theoverlying Si₃ N₄ layer when it is deposited. These cracks and the dopantdepletion result in undesired current leakage paths in the dielectriclayer, which effectively increases the minimum cell nitride thicknesswhich can be used, and thus lowers the capacitance of the depositedfilm. This counters the goal of maximized capacitance in minimum space.Alternate materials to Si₃ N₄ have been proposed, but are difficult tointegrate into existing process flows.

Accordingly, it would be desirable to develop processes and capacitorconstructions which enable continued use of rough polysilicon forcapacitor plates and continued use of Si₃ N₄ for the capacitordielectric.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

The FIGURE is a diagrammatic cross sectional view of a semiconductorwafer fragment in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a method of forming acapacitor comprises the following steps:

providing a node to which electrical connection to a capacitor is is tobe made;

providing a first electrically conductive capacitor plate over the node;

providing a predominately amorphous electrically conductive layer overthe first capacitor plate;

providing a capacitor dielectric layer over the amorphous electricallyconductive layer; and

providing a second electrically conductive capacitor plate over thecapacitor dielectric layer.

In accordance with another aspect of the invention, a capacitorcomprises:

a first electrically conductive capacitor plate;

a predominately amorphous electrically conductive layer over the firstcapacitor plate;

a capacitor dielectric layer over the amorphous electrically conductivelayer; and

a second electrically conductive capacitor plate over the capacitordielectric layer.

In accordance with still a fuirther aspect of the invention, a capacitorcomprises:

a first electrically conductive capacitor plate, the capacitor platecomprising an outer layer of rough hemispherical grain polysilicon;

a predominately amorphous electrically conductive layer over thehemispherical grain polysilicon;

a capacitor dielectric layer over the amorphous electrically conductivelayer; and

a second electrically conductive capacitor plate over the capacitordielectric layer.

Referring to the figure, a semiconductor wafer fragment in process isindicated generally with reference numeral 10. Such comprises a bulksubstrate region 12 and an active area diffision region 14. Aninsulating dielectric layer 16, typically borophosphosilicate (BPSG), isprovided atop substrate 12. A contact opening 18 is provided therein,and is filled with a conductive plugging material 20. Example preferredmaterials would include tungsten or conductively doped polysilicon. Plug20 and layer 16 have been planarized, with plug 20 constituting a nodeto which electrical connection to a capacitor is to be made.

Numeral 25 designates such a capacitor construction. Such comprises afirst electrically conductive capacitor plate 26 comprising conductivelydoped polysilicon. Typically and most preferably in accordance with theinvention, layer 26 comprises one or more layers of polysilicon, withthe outer layer being hemispherical grain polysilicon having a veryroughened outer surface for maximizing capacitance. As described above,such roughened polysilicon outer surface exposes a considerable amountof polycrystalline grain triple points. An example and preferredthickness for composite layer 26 is from 400 Angstroms to 1000Angstroms.

A predominately amorphous electrically conductive layer 28 is providedover first capacitor plate 26. An example and preferred material ismetal organic chemical vapor deposited TiC_(x) N_(y) O_(z), where "x" isin the range of from 0.01 to 0.5, and "y" is in the range of from 0.99to 0.5, and "z" is in the range of from 0 to 0.3, with the sum of "x","y" and "z" equalling about 1.0. Most preferably, the depositionutilizes a gaseous titanium organometallic precursor of the formulaTi(NR₂)₄, where R is selected from the group consisting of H and acarbon containing radical. Example and preferred deposition conditionsare from 200° C. to 600° C., and from 0.1 to 100 Torr to produce thedesired predominately amorphous layer. An example and preferredthickness for layer 28 is from 50 to 100 Angstroms. A specific exampleis to use tetrakisdimethylamido titanium (TDMAT) at 450° C., and 93.3Torr in a cold wall chemical vapor deposition reactor.

Also most preferably, "z" will be equal to zero. Unfortunately however,oxygen can undesirably become incorporated in the deposited film when itis exposed to oxygen, even ambient air. This incorporated oxygenundesirably affects conductivity. Accordingly, exposure to oxygen ispreferably minimized until the subject film is covered by subsequentlayers which can effectively act as a barrier to oxygen incorporation.

The conductively deposited amorphous layer provides a desired functionof covering exposed crystalline triple points such that their presencedoes not propagate within and through a subsequently depositeddielectric layer. Such will facilitate continued use of Si₃ N₄ in higherlevel integration density capacitors.

A capacitor dielectric layer 30, preferably Si₃ N₄, is provided overamorphous electrically conductive layer 28. An example and preferredthickness is from 30 Angstroms to 80 Angstroms. Subsequently, a secondelectrically conductive capacitor plate 32 is provided over capacitordielectric layer 30. Example materials for layer 32 include conductivelydoped polysilicon, or the above described TiC_(x) N_(y) O_(z). Anexample and preferred thickness for plate 32 is 1000 Angstroms.

The invention arose out of concerns and problems associated with cracksin capacitor dielectric layers resulting from triple points inunderlying polysilicon films, and to dopant depletion effects inpolysilicon films in capacitors. However, the artisan will appreciateapplicability of the invention to capacitor constructions and capacitorfabrication methods using conductive plates constituting materials otherthan polysilicon. For example, other conductive plate materials mightgenerate a sufficiently roughened surface at the dielectric layerinterface to result in crack propagation in the dielectric layer.Application of an amorphous conductive layer over such conductive platesprior to provision of the dielectric layer can preclude crackpropagation in the such dielectric layer.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A capacitor comprising:a first electrically conductivecapacitor plate; a predominately amorphous electrically conductive layerover the first capacitor plate and wherein the amorphous electricallyconductive layer comprises TiC_(x) N_(y) O_(z), and wherein "x" is about0.01 to about 0.5, "y" is about 0.99 to about 0.5, and "z" is about 0 toabout 0.3, with the sum of "x", "y" and "z" equaling about 1.0; acapacitor dielectric layer over the predominately amorphous electricallyconductive layer and which comprises Si₃ N₄ ; and a second electricallyconductive capacitor plate over the capacitor dielectric layer.
 2. Acapacitor comprising:a first electrically conductive plate comprising anouter layer of rough hemispherical grain polysilicon; a predominatelyamorphous electrically conductive layer over the hemispherical grainpolysilicon, the predominately amorphous electrically conductive layercomprising TiC_(x) N_(y) O_(z), and wherein "x" is about 0.01 to about0.5, "y" is about 0.99 to about 0.5, and "z" is 0 to about 0.3, with thesum of "x", "y", and "z" equaling about 1.0; a capacitor dielectriclayer over the predominately amorphous electrically conductive layercomprising Si₃ N₄ ; and a second electrically conductive capacitor plateover the capacitor dielectric layer.